Project Summary/Abstract Suicide is among the leading causes of death worldwide, and the risk of suicide is highest in the period immediately following discharge from inpatient psychiatric care. Once patients leave inpatient care, the skills learned during treatment may be difficult to use during the highly distressing time leading up to and during suicidal thoughts and behaviors, which may frequently occur during the time immediately after they are discharged. Surprisingly, current treatments are not designed to be effective during a suicide crisis. Interventions that can reduce the risk of suicidal thoughts and behaviors, both in general and specifically during the post-discharge period, should (1) be easily adhered to and (2) be particularly accessible and efficient during a suicide crisis. The goal of this study is to test an innovative new intervention that uses two new technologies, ecological momentary intervention (EMI) and wearable physiological monitoring to deliver the Unified Protocol (UP) - a transdiagnostic cognitive behavioral therapy. Delivery of this brief intervention will happen not just at certain times or when triggered by the participant, but also in response to physiological changes that signal intense distress (i.e., changes in electrodermal activity over a short period). EMI and physiological monitoring are uniquely suited for adherence and accessibility during a suicide crisis because more than 80% of Americans aged 18-49 carry a smartphone with them throughout the day, and because the study will use a physiological monitoring device worn unobtrusively on the wrist like a watch. The UP is uniquely suited for efficacy because it is a short-term, skills-based treatment that focuses on teaching adaptive responses to intense emotion (such as the intense emotion that characterizes a suicide crisis). Moreover, initial findings support the use of an adapted brief UP intervention with suicidal inpatients. The project will have three phases: (1) a small uncontrolled pilot of intervention that will then (2) be modified based on insights gleaned from the pilot, and finally (3) tested in a larger randomized controlled trial (RCT). Participants in the uncontrolled pilot will be 25 inpatients and participants in the RCT will be 150 inpatients (n = 75 each in treatment as usual [TAU] plus intervention and TAU plus assessment [i.e., control] groups) from the Massachusetts General Hospital Inpatient Psychiatric Service. The intervention will consist of four in-person inpatient therapy sessions and smartphone-based EMI with physiological monitoring for the duration of participants' inpatient stay and the high-risk 28-day post-discharge period, as well as several inpatient sessions aimed at delivering core EMI content and training participants on the use of the EMI. The project's long-term aims are to (1) conduct a small pilot test of the intervention, (2) conduct a randomized controlled trial to test the effects of the intervention, and (3) to explore context- specific efficacy of the intervention to inform future studies of personalized interventions.